1. Field of the Invention
The present invention relates to a semiconductor laser device.
2. Description of the Prior Art
In recent years, a semiconductor laser device having a short wavelength has been developed for the purpose of application to, e.g., a high density optical disc system, a high speed laser printer, and a bar code reader. Among such semiconductor laser devices each having a short wavelength, in particular, an InGaAlP series semiconductor laser device having an oscillation wavelength in a 0.6 .mu.m band has received a great deal of attention as a promising device.
In order to use a semiconductor laser device as a light source for optical information processing, transverse mode control must be performed. The present inventors manufactured a ridge-buried type semiconductor laser device shown in FIG. 1 as an InGaAlP series semiconductor laser device having a transverse mode control structure to confirm fundamental transverse mode oscillation.
Referring to FIG. 1, an n-type GaAs buffer layer 2, an n-type InGaAlP cladding layer 3, an InGaAlP active layer 4, a p-type InGaAlP cladding layer 5, a p-type InGaP cap layer 6, and a p-type GaAs contact layer 7 are sequentially stacked on an n-type GaAs substrate 1. Electrodes 8a and 8b are formed on both surfaces of the above structure.
When the p-type InGaAlP cladding layer 5 contains a large amount of Al, a large hetero barrier is present at the hetero junction interface between the p-type GaAs contact layer 7 and the p-type InGaAlP cladding layer 5 to cause voltage drop. In view of this, when a p-type InGaP layer having an intermediate band gap as compared with those of p-type GaAs and p-type InGaAlP is formed at the hetero junction interface, a voltage drop can be decreased. In the semiconductor laser device shown in FIG. 1, utilizing such a decrease in voltage drop, the p-type InGaP cap layer 6 is formed at only the interface between the p-type GaAs contact layer 7 and the p-type InGaAlP cladding layer 5, formed on a ridge portion of the p-type InGaAlP clad layer 5, thus blocking a current. In addition, a light guide and a transverse mode are stabilized by forming a ridge in the p-type clad layer 5, and by arranging the p-type GaAs contact layer 7 close to the InGaAlP active layer 4 outside the ridge.
A method of manufacturing the above-mentioned semiconductor laser device will be described hereinafter with reference to FIGS. 2A and 2B.
First MOCVD (metal organic chemical vapor deposition is performed to sequentially form the n-type GaAs buffer layer 2, the n-type InGaAlP cladding layer 3, the InGaAlP active layer 4, the p-type InGaAlP cladding layer 5, and the p-type InGaP cap layer 6 on the n-type GaAs substrate 1. Then, a resist pattern 9 is formed on the above structure (FIG. 2A).
Using the resist pattern 9 as a mask, the p-type InGaP cap layer 6 is etched using a stirrer in an aqueous solution containing Br.sub.2 and HBr. In addition, the p-type InGaAlP cladding layer 5 is etched by hot phosphoric acid at 60.degree. to 80.degree. C. to form a ridge (FIG. 2B).
After the resist pattern 9 is removed, the p-type GaAs contact layer 7 is formed by second MOCVD, thus completing a ridge-buried type semiconductor laser device shown in FIG. 1.
The semiconductor laser device thus manufactured is promising as a device having excellent performance. However, when the above-mentioned manufacturing method is employed, it is difficult to manufacture the device at high production yield. More specifically, in the above-mentioned etching process, it is difficult to control a thickness h of each portion of the p-type InGaAlP cladding layer 5 located on both sides of the ridge, which largely affects transverse mode control, due to unstability of an etching rate. In addition, a large variation in etching amount in the wafer surface occurs.